The proposed research is directed toward a determination of the lymphocyte surface structure of the various lymphocyte populations in the rabbit and in the human. This would be accomplished using mitogen and antibodies to these determinants as probes. Studies would be conducted on the surface of normal lymphocytes and related to the surface changes which occur during transformation and as a result of immunization. The influence of hormones produced by the lymphoid system on the differentiation of lymphocyte populations would be studied. The effect of other hormones (corticosteroids, etc.,) on the development of lymphocyte surface structures would also be studied. Antigens specific to the various lymphocyte populations would be isolated, characterized and studied to evaluate their function. The transformation process itself would be studied. The effect of the valence of different mitogens would be determined. The orientation of receptors on the lymphocyte would be studies using membrane trace- labeling techniques. The capping phenomenon would be studied in an attempt to relate transformation to the sequential formation of caps. Such studies would center on attempts to purify and functionally characterize capped cells. In all of these studies antiserum inhibitory of the response of a lymphocyte subpopulation would be used to approach the function of these cells. Finally the effect on a cell of an inhibitory or a stimulatory molecule would be studied to determine their mode of action.